A substrate processing apparatus used for the purposes described above normally comprises a processing unit that includes a plurality of processing chambers where a specific type of processing is executed on substrates such as semiconductor wafers (hereafter may be simply referred to as “wafers”) and a transfer unit connected to the processing unit via at least one load-lock chamber (see Japanese Laid Open Patent Publication No. 2002-237507 (reference literature 1), for instance).
The processing unit in a cluster tool-type substrate processing apparatus may be constituted by connecting with a high level of airtightness the plurality of processing chambers and load-lock chambers around a common transfer chamber assuming a polygonal shape, as shown in FIG. 6 of reference literature 1. Inside the common transfer chamber, a processing unit-side transfer mechanism constituted with a transfer arm and the like is disposed and wafers are transferred between the plurality of processing chambers and the load-lock chambers by the processing unit-side transfer mechanism. A transfer unit-side transfer mechanism also constituted with a transfer arm and the like is installed at the transfer unit, and wafers are transferred between a cassette container (substrate storage container) containing wafers and the load-lock chambers.
A wafer in the cassette container to undergo the specific type of processing in such a substrate processing apparatus is first transferred out of the cassette container by the transfer unit-side transfer mechanism at the transfer unit. The unprocessed wafer having been transferred out of the cassette container is then delivered to a positioning device (e.g., an orienter or a pre-alignment stage) disposed in the transfer unit for positioning, before it is transferred into the load-lock chamber. Once the unprocessed wafer is correctly positioned, it is transferred out of the positioning device and delivered into the load-lock chamber.
The unprocessed wafer having been transferred into the load-lock chamber is transferred out of the load-lock chamber by the processing unit-side transfer mechanism, is delivered into a processing chamber where it undergoes the specific type of processing. Once the processing is completed in the processing chamber, the processed wafer is transferred out of the processing chamber by the processing unit-side transfer mechanism and is returned to the load-lock chamber. The processed wafer having been returned to the load-lock chamber is delivered back into the cassette container by the transfer unit-side transfer mechanism.
Even while the processing is in progress in the individual processing chambers, unprocessed wafers are constantly transferred out of the cassette containers and are made to wait in standby in the common transfer chamber, the load-lock chambers, the positioning device and the like, since it is desirable to maintain a continuous flow of unprocessed wafers waiting in standby at closest possible positions to the processing chambers to assure maximum processing throughput from the processing chambers in the substrate processing apparatus. Once the processing on a given wafer is completed in a processing chamber, the processed wafer is immediately taken back into the cassette container and the unprocessed wafers having been waiting in standby are sequentially delivered so as to transfer the unprocessed wafer next in line immediately into the processing chamber.
In addition, when wafers are processed concurrently in the individual processing chambers, the optimal transfer timing with which wafers are to be transferred from the cassette container to undergo the processing in the processing chambers needs to be determined so as to improve the operation rate of each processing chamber. In the related art, the lengths of remaining processing time to elapse before the processing in progress in the individual processing chambers ends are compared and the unprocessed wafer in the cassette container designated to be processed in the processing chamber with the shortest remaining time is detected and transferred out of the cassette container. Since the processing chamber with the shortest remaining processing time becomes available to process the next wafer the soonest, the wafer to be processed in the processing chamber with the shortest remaining time is transferred out from the cassette container first and, as a result, the operation rate of each processing chamber is improved.
Different types of processing such as etching and film formation processing are often executed in the individual chambers. Even when a single type of processing is executed in the plurality of processing chambers, the processing is often executed under varying processing conditions. Thus, the lengths of time required to process a single wafer in the various processing chambers, the length of time to elapse after a wafer is delivered into a given processing chamber until the wafer processing is completed and the wafer is transferred out of the processing chamber so that the processing chamber becomes available for the next wafer, are not always uniform.
However, in the substrate processing apparatus in the related art described above, the lengths of remaining processing time to elapse before the processing in the individual processing chambers is completed alone are considered and the unprocessed wafer corresponding to the processing chamber with the shortest remaining time is first transferred out of the cassette container, without factoring in the varying lengths of time required to process wafers in the different processing chambers.
If the remaining processing time in a processing chamber where wafers are processed over a relatively long time is shorter than the remaining processing time in a processing chamber where the wafer processing is completed relatively quickly, a wafer corresponding to the processing chamber where the wafer processing takes longer is first transferred out of the cassette container and such a wafer may be kept waiting in standby at the common transfer chamber, the load-lock chamber or the positioning device, delaying the transfer of the wafer for the processing chamber with the shorter processing time out of the cassette container. Under such circumstances, the transfer system in the related art may become counterproductive and reduce both the operation rates of the individual processing chambers and the throughput of the substrate processing apparatus.
More specifically, let us consider processing requiring a greater length of time and processing that can be completed relatively quickly being executed concurrently in a processing chamber P1 and a processing chamber P2 respectively. If the remaining processing time at the processing chamber P1 where the processing takes a longer time is less than the remaining time at the processing chamber P2, the wafer WP1 to undergo the processing in the processing chamber P1 will be the next wafer to be transferred out from the cassette container.
Under such circumstances, another wafer to undergo the processing in the processing chamber P1 is already waiting in standby in, for instance, the common transfer chamber. Thus, the wafer WP1 transferred out of the cassette container upon completion of the processing in the processing chamber P1 cannot be processed immediately, since another wafer having already been waiting in standby at the common transfer chamber, the load-lock chamber, the positioning device or the like is next delivered to the processing chamber P1 to undergo the processing and the wafer WP1 transferred out from the cassette container now needs to wait in standby at the common transfer chamber, the load-lock chamber, the positioning device or the like until the processing of the other wafer delivered into the processing chamber P1 ahead of the wafer WP1 is completed.
In this situation, even if the processing at the processing chamber P2 requiring the shorter length of processing time is completed immediately afterwards and the processing chamber P2 becomes available, a wafer WP2 to be processed in the processing chamber P2 where the processing is completed quickly cannot be transferred out of the cassette container. As a result, an unnecessary idle time occurs in the processing chamber P2 with the shorter processing time, which reduces the operation rate of the processing chamber P2 to lead to a reduction in the throughput of the substrate processing apparatus.